One known such apparatus is described in South African Patent Specification No. 83/4727 (Rintoul). It comprises three heating columns within which the particulate material to be heated is contained and three pairs of electrodes arranged respectively within the columns, the electrodes being connected to a three phase power supply so that current can pass through the material in the columns to heat such material. This apparatus operates on batch production with the contents of the columns treated individually and then discharged.
Another such known apparatus is described in U.S. Pat. No. 4,192,962 (Nakao). This is a device for very small scale production with a high electric power to mass of carbon treated ratio. It comprises a pair of electrodes in the form of annular rings arranged axially spaced from one another and located against the side of a single column with the inside edges of the electrodes spaced from the inner wall of the column. Further such apparatusses are disclosed in U.S. Pat. Nos. 4,624,003 (Eirich et al) and 4,261,857 (Nakao) where the electrodes are arranged axially above each other but with the electrodes located at the sides of the column. In U.S. Pat. No. 4,261,857 (Nakao) there is also shown a column with the electrodes at the same level and the same arrangement is shown in U.S. Pat. No. 3,025,385 (Tanaka).
I have found that great care is required to ensure even heating of the granules across the area of the column especially when it is desired that the column should treat the granules on a continuous basis.